1. Field of the Invention
This invention relates to a disc record/reproduce apparatus with a brushless dc motor which does not include a separately dedicated position sensor.
2. Description of the Prior Art
A disc record/reproduce apparatus is known which comprises a brushless dc motor (synchronous motor) for rotating a record disc. In such apparatus, a dc synchronous motor having no position sensor can be used wherein drive currents of windings of the dc synchronous motor are produced by switching drive transistors in response to detection of back-electromotive forces developed at windings of the dc synchronous motor during rotation of the brushless dc motor. Such brushless dc motor is disclosed in Japanese Patents Publication Nos. 56-33953 and 61-3193.
Another disc record/reproduce apparatus with a dc synchronous motor apparatus including two position detection means of the brushless dc motor for switching drive currents to rotate and to control a rotational speed is known. One position detection means is carried out by a voltage drop at a common resistor for supplying a drive current to windings during start-up of the motor. This control is switched over to the second position detection means which uses a position signal recorded on the record disc. i.e., a sector signal, because such a voltage drop cannot provide position information at a speed higher than a given value. This technique is disclosed in Japanese Patent application provisional publication 63-69489.
However, in the first mentioned prior art disc record/reproduce apparatus, generally, control of such apparatus is carried out by a microprocessor, and thus, the microprocessor becomes too busy because of execution of communication with an external computer, data processing, position control of actuator in addition to switching control of drive currents of the dc synchronous motor. Therefore, there is a drawback that an overload occurs on the processing of a microprocessor.
In the second mentioned prior art disc record/reproduce apparatus, there are drawbacks that power consumption is large because the head position should be controlled or maintained always, even in a standby mode, and the brushless dc motor cannot be inspected without the disc where the position signal has been written.